1. Field of the Invention
The present invention relates generally to stimulating medical devices and, more particularly, to a flexible implantable electrode assembly for a stimulating medical device.
2. Related Art
Hearing loss is generally of two types, namely conductive and sensorineural. The treatment of both of types of hearing loss has been quite different, relying on different principles to deliver sound signals to be perceived by the brain as sound. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. In such cases, hearing loss is often improved with the use of conventional hearing aids, which amplify the sound so that acoustic information reaches the cochlear hair cells. Such hearing aids utilize acoustic mechanical stimulation, whereby the sound is amplified according to a number of varying techniques, and delivered to the inner ear as mechanical energy. This may be through a column of air to the eardrum, or through direct delivery to the ossicles of the middle ear.
On the other hand, sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which are needed to transduce acoustic signals into auditory nerve impulses. Individuals suffering from this type of hearing loss are unable to derive any benefit from conventional hearing aid systems regardless of the volume of the acoustic stimulus. This is because the natural mechanisms for transducing sound energy into auditory nerve impulses are either absent or damaged. In such cases, Cochlear™ implants (also referred to as Cochlear™ devices, Cochlear™ prostheses, Cochlear™ implant systems, and the like; simply “cochlear implants” herein) have been developed to provide the sensation of hearing to such individuals. In cochlear implants, electrical stimulation is provided via stimulating electrodes positioned as close as possible to the nerve endings of the auditory nerve, essentially bypassing the hair cells in a normally functioning cochlea. The application of a stimulation pattern to the nerve endings causes impulses to be sent to the brain via the auditory nerve, resulting in the brain perceiving the impulses as sound.
More recently, there has been an increased interest in Electro-Acoustical Stimulation (EAS) in which electrical stimulation of the cochlea is used in conjunction with acoustical stimulation. It is relatively common in hearing impaired individuals to experience sensorineural hearing loss for sounds in the high frequency range, and yet still be able to discern sounds in the middle to low frequency range, through the use of a conventional hearing aid, or naturally. Traditionally, in the majority of such cases, the recipient would only receive treatment to preserve and improve the hearing for the middle to low frequency sounds, most probably via a conventional hearing aid, and little would be done to attempt to restore the hearing loss for the high frequency sounds. This is due to the potential trauma caused by the implantation of an electrode assembly into the cochlea. Only if the individual lost the ability to perceive middle to low frequency sounds would consideration then be given to restoring the hearing loss for the high frequency sounds, in which case a cochlear implant would be considered a possible solution.